Worcester Bosch CDi RSF Fault codes & diagnostics

11 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 30 kW 1997-2005 Discontinued
GC Numbers 47-311-3547-311-5847-311-5947-311-96

Replaced by: CDi Classic

Download the Worcester Bosch CDi RSF manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 9 High
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-311-35 28 CDi RSF 1997–2002
47-311-58 35 CDi II RSF 2001–2005
47-311-59 35 CDi II RSF 2001–2005
Just want the most common Worcester Bosch CDi RSF faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 11 documented codes

Tap any card for details

A1

Your boiler has stopped because there isn't enough water circulating inside the system to keep it running safely.

High DIY-safe £80-150

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1 bar, your system needs topping up.
  2. Locate the filling loop (usually a silver braided hose under the boiler) and open the valves to let water in until the needle reaches 1.5 bar.
  3. Bleed your radiators to remove any trapped air, then re-check the pressure gauge and top up again if it has dropped.

Parts commonly replaced

  • Central heating pump
  • Pressure relief valve
  • Pressure gauge

Related codes

Full explanation for A1
A2

Your boiler is struggling to accurately measure the temperature of the water it is heating, so it has stopped providing hot water to be on the safe side.

High Engineer only £120-200

Parts commonly replaced

  • Hot water NTC sensor
  • Wiring harness

Related codes

Full explanation for A2
A7

Your boiler is struggling to accurately measure the temperature of the water inside it because a sensor has stopped sending a proper signal.

High Engineer only £120-200

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

Full explanation for A7
b1

Your boiler's computer is struggling to identify the specific configuration chip that tells it how to operate correctly.

High Engineer only £120-200

Parts commonly replaced

  • Code plug
  • Printed Circuit Board (PCB)

Related codes

Full explanation for b1
C1

Your boiler has detected that the internal fan is moving too slowly to safely vent waste gases, so it has stopped working as a precaution.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Full explanation for C1
C6

Your boiler has detected that the fan, which is essential for safely venting exhaust gases, is not spinning at the correct speed.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Full explanation for C6
E2

Your boiler has lost the ability to read the temperature of the water used for your radiators, causing it to shut down for safety.

High Engineer only £150-250

Parts commonly replaced

  • NTC Sensor
  • Wiring harness

Related codes

Full explanation for E2
E9

Your boiler has detected that it is overheating and has automatically switched itself off to prevent damage or dangerous pressure levels.

High Engineer only £150-300

Parts commonly replaced

  • High limit thermostat
  • Central heating pump
  • Primary heat exchanger

Related codes

Full explanation for E9
EA

Your boiler is failing to light the internal flame needed to heat your home's water.

High Engineer only £120-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

Full explanation for EA
F7

Your boiler’s internal safety sensor thinks a flame is present even though it is supposed to be switched off, which has caused the system to shut down to prevent a dangerous situation.

Emergency Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Flame sensing electrode

Related codes

Full explanation for F7
FA

Your boiler has detected that a flame is still burning even though it has tried to turn the gas supply off, which indicates a serious safety sensor issue.

Emergency Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Ionisation electrode

Related codes

Full explanation for FA